1. Field of the Invention
The present invention relates to a light emitting device housing semiconductor light emitting elements such as light emitting diodes (LEDs), and to its method of manufacture.
2. Description of the Related Art
In recent years, use of lower power consuming light emitting diodes (LEDs) in place of conventional incandescent light bulbs has been increasing in applications such as general lighting (illumination fixtures), and the range of applications is expanding. Within those applications, to improve the light extraction efficiency of secondary optics in apparatus such as spotlights and light projecting systems, there is demand for LEDs that emit high output, high quality light from a small intense light emitting area with little luminance and color (chromatic) non-uniformity across the light emitting surface.
As a technique to reduce light emission non-uniformities, the method of diffusing light by including filler in the light emitting element encapsulating material is known. For example, design to implement a white light emitting diode (LED) leads to consideration of a light emitting device that combines a blue LED with yellow-fluorescing yttrium-aluminum-garnet (YAG, Y3Al5O12) fluorescent material, which is excited by light emitted by the blue LED. In this light emitting device, YAG fluorescent material is distributed in the resin or other encapsulating material that encapsulates the blue LED mounted inside a mounting cavity. In addition, by including diffusion material along with the fluorescent material in the encapsulating material, the fluorescent material has better dispersion within the encapsulating resin.
However, color non-uniformity can arise in this type of structure. Specifically, if the optical path length is examined for light prior to exiting the emitting surface of the light emitting device, there is a difference in the path length for light emitted directly upward from the LED and light that obliquely traverses through the encapsulating material after emission from the LED. As a result, the longer the optical path length, the more color-shift occurs due to the increase in light components produced by excitation of fluorescent material distributed in the encapsulating material. Consequently, when the light emitting device is viewed from directly above the light emitting surface, a color-shifted ring can appear around the perimeter of the light emitting surface.
Refer to Japanese Laid-Open Patent Publications 2008-041290, 2008-282754, and 2011-159970.
The present invention was developed to resolve these types of prior art drawbacks. Thus, it is a primary object of the present invention to provide a light emitting device and its method of manufacture that suppresses color non-uniformity and improves the quality of the output light.